1. Field of the Invention
The present application is generally directed to storage systems having one or more storage subsystems or storage units, and more specifically, to preventing the creation of single points of failure in storage systems.
2. Description of the Related Art
In order to maintain the consistency of the data in a storage system, where an existing storage subsystem is to be replaced by a replacement storage subsystem due to failure, obsolescence or a need for maintenance, conventional storage subsystems typically require that all of the I/O to the replaced storage unit be halted. Recently, it has been possible to replace an existing storage subsystem with a replacement storage subsystem without stopping the host I/O, by using N_Port ID Virtualization (NPIV) technology. The path for the I/O connections between a host and a storage subsystem is provided through ports, each having a name or identifier.
NPIV allows for the creation of one or more virtual ports on one physical port. By this port virtualization, NPIV also allows port migrations accompanied by the device, such as host computers, storage system, to change access paths. As explained in U.S. Publication 2010/0070722, by using the multiple port environment, users can migrate data between two storage subsystems without disruption.
However, there are several unresolved issues with regard to the solution proposed by the foregoing publication. For example, for a storage system that utilizes Fiber Channel (FC), suspension of all I/O is required for several seconds in order to logout and re-login. During such a process, the path configuration of the storage subsystem reduces to a single path, which creates a single point of failure should the path be disrupted.
Therefore, there is a need to prevent such a single point of failure.